142 THE OSTEOLOGY AND MYOLOGY 



clear. The triceps of the thigh is the triceps of the arm ; it comprehends both long and 

 short extensoi's of the next segment. The rectus femoris is the scapular head of the 

 triceps, and is the long direct extensor. The vastus externus and vastus internus are 

 respectively the outer and inner humeral heads of the triceps, and are the short direct 

 extensors. 



The peculiar office of the human sartorius is but faintly or not at all foreshadowed in 

 lower mammals. In man a flexor of both thigh and leg, in other mammals, as in the opos- 

 sum, it appears in its true character as accessory long extensor of the leg and indirect 

 flexor of the thigh. Its homologue in the anterior extremity is the de facto slip from the 

 latissimus but de jure distinct muscle, called by Owen omo-anconeus, and by Duvernoy 

 dorso-epitrochlien. 



In the anterior extremity a muscle, ordinarily of moderate size, in this instance ex- 

 tremely small, proceeds fi'om the hsemapophysis to the shaft of the proximal segment of 

 the diverging appendage ; it is the coraco-brachialis. Similarly, in the hind limb, a set of 

 muscles, ordinarily of great size, and in this instance extremely large, proceeds from the 

 same to the same morphological point ; they are the three adductors — magnus, longus and 

 brevis ; and there can be little doubt that collectively they are the homologue of the 

 coraco-brachialis. The tests of position and relation go far toward proving this. It mat- 

 ters nothing that the one has little size or power, and that the other is large and strong. 

 This is a purely teleological modification ; and so is, also, the mutual relation of the two, 

 considered as flexors or extensors ; for the office of these muscles is notoriously variable in 

 different animals. But it so happens in the opossum, from the shape of the parts, that the 

 "adductors" are really powerful extensors, and only slightly adductive ; and that what 

 feeble action the coraco-brachialis has, is also extensive and adductive in about equal parts. 

 The objection, that here are thi'ee muscles in the thigh to one in the ai-m, has little 

 morphological import ; but rather, on the contrary, is a good illustration of teleologi- 

 cal dismemberaient of a muscle — just such a modification as it is in some other cases expe- 

 dient or necessary to take for granted. 



One of the largest muscles or sets of muscles of the anterior extremity has not yet been 

 accounted for — I aUude to the pectoral. Their identification probably hinges upon our 

 determination of the relationships of the clavicle and coracoid to the pubis and ischium. 

 If the clavicle and pubis are the haemal spines, and correspondent, the foregoing 

 identification of the adductors with the coraco-brachialis is apparently most rational ; both 

 these muscles coming from hoemapophyses to the shaft of the first segment of the append- 

 ages ; and there is nothing left to represent the pectorales but the pectineus. This is the 

 view taken by Prof. Wilder. If, however, the clavicle be homologous with the ischium, as 

 Prof. Wyman holds, the inference seems just, that the coraco-brachialis is repeated in the 

 pectineus, and that consequently the pectorales are to be found in the adductors. I pre- 

 sume there is little or no question that the pectorales and coraco-brachialis are to be looked 

 for, if at all, in the pectineus and adductors together ; but a more special determination is 

 rendered difficult by a variety of conditions. In the particular instance of the opossum, 

 for example, the pectineus is really neither pubic nor ischiatic, but arises from the marsu- 

 pial bone ; and part of the origins of the adductors is pubic — that of the magnus alone 

 being essentially ischiatic. 



The cubital flexor system, situated upon the front of the arm, consists essentially of an 



